Frequency dependence of Q in the mantle underlying the shield areas of Eurasia, Part III: The Q model

Abstract

A large set of teleseismic body wave data covering a broad range in frequency was analysed to determine the frequency and depth dependence of Q for P‐ and S‐waves under the northern shield areas of Eurasia. Based on numerous t* estimates for P‐ and S‐waves covering the seismic band between 0.02 and 8 Hz, a Q model of the Eurasian shield was constructed. The data require a model in which Q increases with frequency and which is characterized by Q values in the upper mantle that are generally higher than those of global average models. The model with the best fit includes a minimum in Q between about 100 and 200 km depth and high Q values on the order of thousands throughout most of the deeper mantle. These results are generally consistent with proposed models of attenuation as a thermally activated process which is influenced by the temperature and pressure in the earth. Preliminary results suggest that t* under tectonic regions is higher than t* under shield regions for all frequencies over the 0.02 to 8 Hz frequency range suggesting that Q varies regionally as well as with frequency and depth. Copyright © 1986, Wiley Blackwell. All rights reserved